Sawteeth in the MST reversed field pinch

Details Sawteeth in the MST reversed field pinch Sawteeth in the MST reversed field pinch

Sep 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990phdt........14b&link_type=abstract

Ph.D. Thesis Wisconsin Univ., Madison.

Astronomy and Astrophysics

Astrophysics

Dynamo Theory, Magnetic Fields, Plasma Currents, Plasma Diagnostics, Reverse Field Pinch, Sawtooth Waveforms, Tokamak Devices, Toroidal Plasmas, Astrophysics, Current Density, Diffusivity, Nonlinear Systems, Plasma Density, Plasma Temperature, Reynolds Number, Universe

Scientific paper

A dynamo mechanism has been used in astrophysics to explain the self-generation of the magnetic fields observed throughout the universe. This same type of phenomenon is believed to occur in the reversed field pinch (RFP) plasmas. The RFP dynamo has been a major theoretical and experimental investigation since the first observations of the self-reversal process in early pinch research. A discrete dynamo event has been observed in the experimental RFP plasmas; this event is termed the RFP sawtooth. This phenomenon is similar to the sawtooth phenomenon observed in tokamak plasmas, but the two events differ in many respects. Both events are a result of the inward diffusion of the plasma current density. This causes the plasma to become unstable to the m = 1 tearing modes. It has been shown theoretically that the nonlinear interaction of these modes can generate the reversed toroidal field in the RFP. This thesis is a study of the RFP sawtooth phenomenon on the MST RFP. This includes experimental observations as well as 1-D numerical simulations of the sawtooth rise-time. During the rise-time of the sawtooth, the plasma is undergoing a purely diffusive process - no dynamo is occurring during this phase. The dynamo only occurs during the sawtooth crash. During the rise-time, the m = 1 modes are observed to grow, and nonlinear interactions are observed prior to the sawtooth crash. At the time of the crash, many of the plasma profiles are flattened; these include the current density, the plasma temperature and the plasma density. The period of the sawteeth is observed to increase with the plasma current, as well as the magnetic Reynolds number, S.

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